A plasma process is essentially performed in manufacturing a semiconductor device. Recently, to meet the requirement for high integration and high speed of LSI (Large Scale Integration), there has been a demand for a more improved microfabrication technique in a semiconductor device forming the LSI.
However, in a capacitively coupled plasma processing apparatus or an inductively coupled plasma processing, generated plasma has a high electron temperature and a region having a high plasma density is limited. Thus, it has been difficult to perform a plasma process that satisfies the requirement for improved microfabrication of the semiconductor device.
In order to achieve such improved microfabrication, it is required to generate plasma having a low electron temperature and a high plasma density. To this end, there has been proposed an apparatus configured to generate surface wave plasma in a processing vessel by a microwave and perform a plasma process on a semiconductor wafer by the surface wave plasma (see, for example, Patent Document 1).
In a plasma processing apparatus described in Patent Document 1, a microwave is transmitted through a coaxial waveguide and radiated into a processing vessel, and by exciting a gas through electric field energy of a surface wave of the microwave, surface wave plasma having a low electron temperature and a high plasma density is generated.
In the plasma processing apparatus of Patent Document 1, however, in order to radiate the microwave into the processing vessel from the coaxial waveguide, a ceiling portion of the plasma processing apparatus has a structure in which a dielectric plate made of, e.g., quartz is provided between the surface wave plasma and an antenna, and a processing gas is supplied into the processing vessel from a sidewall of the processing vessel. Since, however, the processing gas is supplied from a portion other than the ceiling portion, it has been difficult to control a gas flow appropriately. Resultantly, it has been also difficult to control the plasma effectively.
In this regard, Patent Document 2 describes a technique of providing, under an antenna, a shower plate that has a multiple number of gas holes and is made of a dielectric material, and introducing a processing gas vertically downwards into the processing vessel through the shower plate. In this method, a gas flow in the vertical direction is formed within the processing vessel, so that the processing gas may be supplied uniformly and uniform plasma can be generated.
Patent Document 1: Japanese Patent Laid-open Publication No. 2003-188103
Patent Document 2: Japanese Patent Laid-open Publication No. 2005-196994
According to the present inventors, however, in the plasma processing apparatus having the antenna and the shower plate as described in Patent Document 2, for example, it is observed that a film is formed within the holes of the shower plate. If the film is formed within the holes, however, the holes may be blocked.
The reason for the film formation within the holes of the shower plate is because, due to surface wave plasma, an electron temperature at a region in the vicinity of the shower plate is higher than that at a region far from a surface of the shower plate. By way of example, a source gas such as a monosilane (SiH4) gas is excessively decomposed in the vicinity of the shower plate. As a result, the decomposed source gas may be deposited to form a film in hole portions of the shower plate or may become the cause of dust through the gas phase reaction.
The present inventors believed that if the source gas supplied from the shower plate can reach the inside of the processing vessel without passing through the region having the high electron temperature in the vicinity of the shower plate, the film formation or the vapor phase epitaxy in the vicinity of the shower plate could be suppressed.